Many of the radiographic parameters essential to total hip arthroplasty (THA) component performance, such as wear and stability, can be assessed intraoperatively with fluoroscopy. However, even with intraoperative fluoroscopic guidance, the placement of an implant or the reduction of a bone fragment may still not be as close as desired by the user. For example, mal-positioning of the acetabular component during hip arthroplasty can lead to problems. For the acetabular implant to be inserted in the proper position relative to the pelvis during hip arthroplasty requires that the user know the position of the patient's pelvis during surgery. Unfortunately, the position of the patient's pelvis varies widely during surgery and from patient to patient. During trauma surgery, proper fracture management, especially in the case of an intra articular fracture, requires a user to reduce the bone fragment optimally with respect to the original anatomy to: provide the joint the best chance to rehabilitate properly, minimize further long-term damage and, if possible, to regain its normal function. Unfortunately, in a fracture scenario, the original anatomical position of these bone fragments has been compromised and their natural relationship with the correct anatomy is uncertain and requires the user to use his/her best judgment to promote a successful repair and subsequent positive outcome.
Various devices are known to reduce mal-positioning of these surgical components. For example, a transverse acetabular ligament has been suggested as a qualitative marker of the orientation of the acetabulum. (Archbold H A, et al. The Transverse Acetabular Ligament; an Aid to Orientation of the Acetabular Component During Primary Total Hip Replacement: A Preliminary Study of 200 Cases Investigating Postoperative Stability, J Bone Joint Surg BR. 2006 July; 88(7):883-7). However, it has been suggested that the acetabulum may be deteriorated due to arthritis. Others have proposed using a tripod device that uses the anatomy of the ipsilateral hemi pelvis as the guide to position the prosthetic acetabular component. U.S. Patent Publication Number 20090306679. This instrument has three points. The first leg is positioned in the posterior inferior acetabulum, a second leg is positioned in the anterior superior iliac spine and a third leg is positioned on the ileum of the subject. U.S. Patent Publication Number 20090306679. Regarding fracture fixation, or a correction of a deformity or malunion, various devices have also been suggested to support proper reconstruction or reduction of bone fragments. For example, a distal radius volar fixation plate has been suggested to act as an invasive, intraoperative quantitative supporting buttress to fix and provide a reference to the user to help realign the broken bony anatomy.
Most surgical instruments positioning systems are navigated one or several anatomical reference planes that are initially registered in relative position to temporarily implanted fixed markers tracked by a computer system via various methods, such as IR, EMF, etc. The precision of these systems helps users to position instruments and implants with the expectation to improve patient outcomes. The invasiveness of these trackers is minimal but has been documented to lead to fractures and other complications, such as insertion site pain. In addition, the set up is lengthy and adds considerable time to the surgery. Other systems which attempt to register a non-invasive reference plane are extrapolating the plane from a non-anatomical reference, such as the horizontal plane of an operating table. The accuracy of such system has not proved any additional benefit in surgical instrument and implant position. A new way to identify the reference plane in a non-invasive and time effective manner based on known and proven anatomical markers is needed.